Master-oscillator power-amplifier laser system

Abstract

An improved phase conjugate master-oscillator power-amplifier laser system for providing a high-power low-distortion laser output beam. The system includes an improved oscillator such as a ring oscillator which rejects any of the output beam which is inadvertently fed back to the oscillator, thereby preventing unwanted oscillation. The system also includes an attenuator such as a spatial filter or an optical isolator that attenuates any amplified spontaneous emissions that may be reflected from the power amplifier to the oscillator, thereby preventing oscillator degradation that would otherwise result. The invention is particularly well-suited for a laser system which employs an SBS mirror for phase conjugation.

I claim: 
     
       1. A master-oscillator power-amplifier optical system which comprises: a master oscillator comprising ring oscillator means for providing an input laser beam having a predetermined frequency along an input path, said ring oscillator means comprising: (a) an amplifying medium having an input for receiving a forwardly propagating laser beam and amplifying the received beam; and   (b) a plurality of reflector means disposed to receive the amplified beam from the medium along a ring path around the medium and back into the input for further amplification, one of the plurality of reflector means providing the input beam by transmitting a portion of the amplified beam along the input path;     a beam splitter disposed to receive the input beam from said ring oscillator means;   a power amplifier disposed to receive the input beam from said beam splitter and amplify the beam;   a reflector disposed to reflect the beam back through the power amplifier and through the beam splitter to provide an amplified output beam along an output path; and   attenuation means including a frequency filter disposed along the input path for rejecting substantially all of the output beam that propagates back along the input path toward said ring oscillator means.   
     
     
       2. A master oscillator power amplifier optical system comprising: oscillator means for providing an input laser beam along an input path, said oscillator means including a ring oscillator comprising an amplifying medium having an input for receiving a forwardly propagating laser beam and adapted to amplify the received beam, a plurality of reflector means, disposed to receive the amplified beam from the medium and operative to reflect the beam forwardly along a ring path around the medium and back into the input for further amplification, one of the reflector means being operative to provide the input beam by transmitting a portion of the amplified beam along the input path and to reject any of the output beam that propagates back along the input path by reflecting said output beam away from the input path, and polarizing means for polarizing the input beam;   a polarizing separating beam splitter to receive the beam from the oscillator means;   a power amplifier disposed to receive the beam from the beam splitter and amplify the beam;   polarity rotation means for rotating the polarity of the amplified beam;   a phase conjugate mirror responsive to the rotated beam to provide a beam that is a conjugate thereof and to direct the conjugate back through the polarity rotation means whereby the polarity thereof is further rotated to provide a beam having a polarity orthogonal to the polarity of the input beam, back through the amplifier, and thence back through the beam splitter to provide an amplified output beam along an output path; and   oscillator means, including attenuation means comprising a frequency filter for rejecting substantially all of the output beam that propagates back along the input path toward the oscillator means.   
     
     
       3. A master oscillator power amplifier optical system which comprises: ring oscillator means for providing an input laser beam along an input path;   polarizing means disposed along said input path for polarizing the input beam;   a polarization separating beam splitter disposed to receive the beam from the oscillator means;   a power amplifier disposed to receive the beam from the beam splitter and amplify the beam;   polarity rotation means to rotate the polarity of the amplified beam;   an SBS phase conjugate mirror responsive to the rotated beam to provide a beam that is a conjugate thereof and that has a frequency that has been shifted from the predetermined frequency by a shift amount and to direct the conjugate beam back through the polarity rotation means whereby the polarity thereof is further rotated to provide a beam having a polarity orthogonal to the polarity of the input beam, thence back through the amplifier and the beam splitter to provide an amplified output beam along an output path; and   an optical isolator for attenuating any amplified spontaneous emissions that may be introduced into the output beam and transmitted back along the input path toward the oscillator means, said isolator comprising a filter disposed between the oscillator means and the beam splitter and adapted to transmit a beam having a frequency equal to that of the input beam and to attenuate a beam having a frequency equal to that of the conjugate beam.   
     
     
       4. A master-oscillator power-amplifier optical system which comprises: power amplifier means for amplifying a laser beam;   reflector means disposed adjacent to one end of said power amplifier means for reflecting an incident laser beam back through said power amplifier means to provide an amplified output beam along an output path;   a master oscillator comprising ring oscillator means for providing an input laser beam along an input path, said ring oscillator means comprising: an amplifying medium for amplifying a laser beam; and   a plurality of reflector means disposed to reflect an amplified beam provided by said amplifying medium along a ring path and along an input path to said power amplifier means, one of the reflector means being adapted to transmit a portion of the amplified beam along the input path and to reflect the amplified output beam that propagates back along the input path toward said ring oscillator means;     attenuation means for attenuating the output beam that propagates back along the input path toward said ring oscillator means; and   a beam splitter disposed between said ring oscillator means and said power amplifier means for coupling the input beam from said ring oscillator means to said power amplifier means and for coupling said amplified output beam out of said optical system along said output path.   
     
     
       5. A master-oscillator power-amplifier optical system which comprises: power amplifier means for amplifying a laser beam;   reflector means disposed adjacent to one end of said power amplifier means for reflecting an incident laser beam back through said power amplifier means to provide an amplified output beam along an output path;   a master oscillator comprising ring oscillator means for providing an input laser beam along an input path, said ring oscillator means comprising: an amplifying medium for amplifying a laser beam; and   a plurality of reflector means disposed to reflect an amplified beam provided by said amplifying medium along a ring path and along an input path to said power amplifier means, one of the reflector means being adapted to transmit a portion of the amplified beam along the input path and to reflect the amplified output beam that propagates back along the input path toward said ring oscillator means; and     a beam splitter disposed between said ring oscillator means and said power amplifier for coupling the output beam from said ring oscillator means to said power amplifier means and for coupling said amplified output beam out of said optical system along said output path.   
     
     
       6. A master-oscillator power-amplifier optical system which comprises: power amplifier means for amplifying a laser beam;   reflector means disposed adjacent to one end of said power amplifier means for reflecting an incident laser beam back through said power amplifier means to provide an amplified output beam along an output path;   a master oscillator comprising; ring oscillator means for providing an input laser beam along an input path;   an amplifying medium for amplifying a laser beam;   a plurality of reflector means disposed to reflect an amplified beam provided by said amplifying medium along a ring path and along an input path to said power amplifier means, one of the reflector means being adapted to transmit a portion of the amplified beam along the input path and to reflect the amplified output beam that propagates back along the input path toward said ring oscillator means; and     a beam splitter disposed between said ring oscillator means and said power amplifier for coupling the input beam from said ring oscillator means to said power amplifier means and for coupling said amplified output beam out of said optical system along said output path.   
     
     
       7. A master-oscillator power-amplifier optical system which comprises: power amplifier means for amplifying a laser beam;   phase conjugate mirror means disposed adjacent to one end of said power amplifier means for reflecting an incident laser beam back through said power amplifier means to provide an amplified output beam along an output path;   a master oscillator comprising ring oscillator means for providing an input laser beam along an input path; and   a beam splitter disposed between said ring oscillator means and said power amplifier for coupling the input beam from said ring oscillator means to said power amplifier means and for coupling said amplified output beam out of said optical system along said output path.   
     
     
       8. A master-oscillator power-amplifier optical system which comprises: power amplifier means for amplifying a laser beam;   phase conjugate mirror means disposed adjacent to one end of said power amplifier means for reflecting an incident laser beam back through said power amplifier means to provide an amplified output beam along an output path;   a master oscillator comprising ring oscillator means for providing an input laser beam along an input path to said power amplifier means, said ring oscillator means comprising isolator means for attenuating amplified energy coupled back into the ring oscillator from the power amplifier means; and   a beam splitter disposed between said ring oscillator means and said power amplifier for coupling the input beam from said master oscillator to said power amplifier means and for coupling said amplified output beam out of said optical system along said output path.   
     
     
       9. The optical system according to claim 1 wherein said ring oscillator means further comprises an optical isolator disposed to receive a beam propagating along the ring path and operative to attenuate that portion of the output beam that propagates back along the input path into said ring oscillator and thence backwardly around the ring path. 
     
     
       10. The optical system according to claim 1 wherein the isolator comprises a Bragg cell isolator. 
     
     
       11. A MOPA optical system according to claim 9 wherein the isolator comprises a magneto-optic "Faraday" isolator. 
     
     
       12. The optical system according to claim 2 wherein said oscillator means further comprises: an optical isolator disposed to receive a beam propagating along the ring path and adapted to attenuate the output beam that propagates back along the input path into the oscillator means and backwardly around the ring path.   
     
     
       13. The optical system according to claim 12 wherein the isolator comprises a Bragg cell isolator. 
     
     
       14. The optical system according to claim 12 wherein the isolator comprises a magneto-optic Faraday isolator. 
     
     
       15. The optical system according to claim 3 wherein the filter comprises a band pass filter. 
     
     
       16. The optical system according to claim 3 wherein the filter comprises a notch filter. 
     
     
       17. The optical system according to claim 3 wherein the filter comprises a high pass filter. 
     
     
       18. The optical system according to claim 3 wherein the optical isolator comprises a filter disposed between the power amplifier and the reflector. 
     
     
       19. The optical systems according to claim 18 wherein the filter comprises a band pass filter. 
     
     
       20. A MOPA optical system according to claim 3 which further comprises a spatial filter disposed along the input path and operative to attenuate amplified spontaneous emissions within said oscillator means. 
     
     
       21. The optical system according to claim 20 which further comprises attenuation means for rejecting the output beam that propagates back along the input path toward the oscillator means. 
     
     
       22. The optical system according to claim 21 wherein the ring oscillator comprises: an amplifying medium having an input for receiving a forwardly propagating laser beam and operative to amplify the received beam;   a plurality of reflector means, disposed to receive the amplified beam from the medium and operative to reflect the beam forwardly along a ring path around the medium and back into the input for further amplification, one of the reflector means being operative to provide the input beam by transmitting a portion of the amplified beam along the input path toward the beam splitter and to reject any of the output beam that propagates back along the input path by reflecting said output beam away from the input path; and   means for polarizing the input beam.   
     
     
       23. The optical system according to claim 22 wherein the ring oscillator means further comprises an optical isolator disposed to receive a beam propagating along the ring path and operative to attenuate any of the output beam that propagates back along the input path into the ring oscillator means and thence backwardly around the ring path. 
     
     
       24. The optical system according to claim 23 wherein the isolator comprises a Bragg cell isolator. 
     
     
       25. The optical system according to claim 24 wherein the isolator comprises a magneto-optic Faraday isolator. 
     
     
       26. The optical system of claim 6 which further comprises: attenuation means for attenuating that portion of said amplified output beam that propagates back along the input path toward said ring oscillator means.   
     
     
       27. The optical system of claim 6 wherein said reflector means comprises phase conjugate mirror means. 
     
     
       28. The optical system of claim 27 wherein said master oscillator comprises: an amplifying medium for amplifying a laser beam; and   a plurality of reflector means disposed to reflect an amplified beam provided by said amplifying medium along a ring path and along an input path to said power amplifier means, one of the reflector means being adapted to transmit a portion of the amplified beam along the input path and to reflect the amplified output beam that propagates back along the input path toward said ring oscillator means.   
     
     
       29. The optical system of claim 28 which further comprises: attenuation means for attenuating that portion of said amplified output beam that propagates back along the input path toward said ring oscillator means.   
     
     
       30. The optical system according to claim 8 which further comprises: attenuation means disposed between said beam splitter and said ring oscillator means for attenuating the portion of the amplified output beam that is coupled along the input path toward said ring oscillator means.   
     
     
       31. The optical system according to claim 30 wherein the isolator comprises a magneto-optic Faraday isolator. 
     
     
       32. The optical system according to claim 30 wherein the isolator comprises a Bragg isolator. 
     
     
       33. The optical system according to claim 30 wherein said attenuation means further comprises: spatial filtering means disposed between said beam splitter and said ring oscillator means for attenuating energy comprising amplified spontaneous emissions present in the amplified output beam that is coupled along the input path toward said ring oscillator means.